1. Field of the Invention
This invention relates to an illuminating apparatus and a method of manufacturing an edge light conductor for use therein. More particularly, the invention relates to an illuminating apparatus comprising an edge light conductor including a plate of transparent or semitransparent optical medium, and light sources opposed to end surfaces of the plate for introducing light inwardly of the plate through the end surfaces. The plate has at least one of front and back surfaces defining a diffusing plane including irregular reflector regions distributed over the diffusing plane. The invention relates also to a method of manufacturing the edge light conductor.
2. Description of the Related Art
This type of illuminating apparatus has a construction as shown in FIG. 12. A plate of transparent or semitransparent optical medium receives light beams b1, b2, b3 and b4 entering through an end surface 2. The plate A has a lower surface defining a diffusing plane 8 including irregular reflector regions 9a and 9b. The beams b1 and b2 are irregularly reflected from the irregular reflector regions 9a and 9b to exit the plate A to illuminate an object.
Light beams, e.g. beams b3 and b4, which do not hit the irregular reflector regions 9 impinge on the upper and lower surfaces of the plate A at incident angles .theta. not exceeding a critical angle .theta.c, to be totally reflected. The incident angles are dependent on the angles at which the beams impinge on the end surface 2 and on the thickness of the plate A. As a result, these beams b3 and b4 continue traveling inside the plate A, instead of exiting the plate A, before reaching the irregular reflector regions 9.
The quantity of exiting light (i.e. illuminating intensity) per unit area of an illuminating plane of the illuminating apparatus is adjustable by varying areas of the irregular reflector regions per unit area of the diffusing plane 8.
The irregular reflector region 9b remote from the end surface 2 has a large irradiated area per unit source area because of a long distance from the light source L. In addition, the beam b2 reaches this irregular reflector region 9b after being considerably attenuated as it travels along an extended optical path through the plate A. Thus, the beam b2 impinges on a unit area of the irregular reflector region 9b in a smaller quantity than the beam b1 impinging on the unit area of the irregular reflector region 9a close to the end surface 2. Naturally, therefore, the irregular reflector region 9b provides a reduced quantity of irregular reflection per unit area.
In order for the illuminating apparatus to have a uniform illuminating intensity throughout the illuminating plane, the quantity of irregular reflection must be uniformed throughout unit areas of the diffusing plane 8.
A plate A in a conventional illuminating apparatus of this defines a diffusing plane 8 including irregular reflector regions 9 as shown in FIG. 13. The irregular reflector regions 9 are distributed such that the areas thereof occupying unit areas of the diffusing plane 8 are larger in positions 8b remote from end surfaces 2 of the plate A than in positions 8a close thereto.
According to the prior art noted above, it is necessary to secure large regions 13 of the diffusing plane 8 in the positions 8a close to the end surfaces 2 where no irregular reflector regions 9 are formed, in order that the irregular reflector regions 9 are larger in the positions 8b remote from the end surfaces 2 than the positions 8a close thereto. These regions 13 are left to be smooth and transparent regions producing little or no effect of irregular reflection.
Thus, the diffusing plane 8 produces the less total quantity of irregular reflection for the regions 13 where no irregular reflector regions 9 are formed. This results in the inconvenience that the illuminating apparatus becomes dark with the illuminating intensity reduced for uniformity. The conventional construction also has a disadvantage of failing to use the light from the light sources effectively.
In the prior art, the quantity of irregular reflection per unit area is adjusted by means of the irregular reflector regions and transparent regions. This inevitably results in lack of uniformity in illuminating intensity over the illuminating plane of the apparatus since the irregular reflector regions and transparent regions produce a great difference in illuminating intensity (contrast). Specifically, the patterns of the irregular reflector regions 9 distributed as shown in FIG. 13 appear on the illuminating plane of the apparatus.